Duetting, aggression and extra-pair paternity in a promiscuous bird species.
The courtship and mating behaviors of the perky Australian red-backed fairy-wren have evolved into nothing short of a free-for-all. The rampant promiscuity of both sexes is legendary.
What’s a fairy-wren to do to keep from wasting energy raising another male’s chicks? New research from scientists at the Cornell University Lab of Ornithology provides a surprising answer: Sing with your mate.
“The result was not expected at all,” said Daniel Baldassarre, an author of the study published Feb. 24 in the journal Biology Letters. He was a Cornell graduate student at the time of the study and is a National Science Foundation postdoctoral fellow at the University of Miami. “In fact, we were actually looking into whether more aggressive males did better at preventing extra-pair matings with their mate than more timid males. We thought the aggressive males would be cuckolded less often.”
The scientists tested their theory in the subtropical grassland and open woodland habitats favored by a population of color-banded red-backed fairy-wrens just outside Brisbane in Queensland, Australia. DNA paternity testing on the offspring from nests in the study site found 60 percent contained young sired by a male who did not share their nest.
To test the aggression hypothesis, the scientists positioned fake fairy-wrens in the bushes and played male song recordings. Some wrens were fierce in their territorial defense, physically attacking the fake birds to drive them off. Others were wary. But in the end, it made no difference. Whether lion or lamb, on average the males got cuckolded just as often.
But in addition to measuring levels of aggression, the scientists also measured how quickly the pair began a duet and how often they sang duets after detecting an intruder. Those who reacted quickly and sang duets more are said to have a “strong” duet-singing response. Others were slower on the uptake.
“We found that pairs with a strong duet response had lower rates of cuckoldry,” said study author and Cornell Lab of Ornithology scientist Emma Greig. “Pairs were less likely to mate outside of their pair bond when they sang together more.”
“The male and female will immediately fly together and perch on a branch right next to each other and start belting out these duets,” added Baldassarre. “If the males are particularly riled up, they will do this ‘puff-back’ display, raising the orange or red feathers on their back to the intruder. While singing duets, their heads are thrown back to the sky with their beaks wide open.”
Even when pairs have a strong duet response, sometimes the mates still stray, but it does increase the likelihood that they’re raising mostly their own genetic offspring.
What exactly is going on during this duet and who is taking the lead? That’s the next big question in order to figure out what function the duets serve.
“The big picture question is about how animals make mating decisions,” Greig explained. “Our results suggest the females are deciding what males to cuckold. Females are either being influenced by their mate’s songs, or females are indicating their own choice by singing with their mates more. We need more detailed work to distinguish these alternatives.”
Funding: Support for the new study came from Macaulay Library, Cornell Lab of Ornithology.
Source: Melissa Osgood – Cornell University
Image Source: The images are credited to Joseph Welkin and Emma Grieg.
Original Research: Abstract for “The couple that sings together stays together: duetting, aggression and extra-pair paternity in a promiscuous bird species” by Daniel T. Baldassarre, Emma I. Greig, and Michael S. Webster in Biology Letters. Published online February 24 2016 doi:10.1098/rsbl.2015.1025
The couple that sings together stays together: duetting, aggression and extra-pair paternity in a promiscuous bird species
When individuals mate outside the pair bond, males should employ behaviours such as aggression or vocal displays (e.g. duetting) that help assure paternity of the offspring they care for. We tested whether male paternity was associated with aggression or duetting in the red-backed fairy-wren, a species exhibiting high rates of extra-pair paternity. During simulated territorial intrusions, aggression and duetting were variable among and repeatable within males, suggesting behavioural consistency of individuals. Males with quicker and stronger duet responses were cuckolded less often than males with slower and weaker responses. In contrast, physical aggression was not correlated with male paternity. These results suggest that either acoustic mate guarding or male–female vocal negotiations via duetting lead to increased paternity assurance, whereas physical aggression does not.
“The couple that sings together stays together: duetting, aggression and extra-pair paternity in a promiscuous bird species” by Daniel T. Baldassarre, Emma I. Greig, and Michael S. Webster in Biology Letters. Published online February 24 2016 doi:10.1098/rsbl.2015.1025